I might take a stab at this next week.

Handing over :)

Code pointer: The list of things that use the measurement already is here:
https://code.google.com/p/chromium/codesearch#chromium/src/components/data_use_measurement/core/data_use_user_data.h&l=26

Clarification: we want to track snippets data usage; we're not interested (at the moment) in tracking other NTP data usage, such as for the remote NTP. Correct?

Yes exactly, this is for NTP snippets only.

All written; waiting on external reviewer.

All written; reviewed; now waiting on different external reviewer.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8e6034b8270b33a5820253af2ca210dc4dff06e8

commit 8e6034b8270b33a5820253af2ca210dc4dff06e8
Author: sfiera <sfiera@chromium.org>
Date: Mon May 02 10:44:06 2016

Add "NTPSnippets" to data usage tracker enum.

Make a small, unrelated spelling correction in the header.

BUG= 601380 

Review-Url: https://codereview.chromium.org/1875073002
Cr-Commit-Position: refs/heads/master@{#390912}

[modify] https://crrev.com/8e6034b8270b33a5820253af2ca210dc4dff06e8/components/data_use_measurement/core/data_use_user_data.cc
[modify] https://crrev.com/8e6034b8270b33a5820253af2ca210dc4dff06e8/components/data_use_measurement/core/data_use_user_data.h
[modify] https://crrev.com/8e6034b8270b33a5820253af2ca210dc4dff06e8/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4bbaba9313c70ca1b5f332ce4458192335d2f14d

commit 4bbaba9313c70ca1b5f332ce4458192335d2f14d
Author: sfiera <sfiera@chromium.org>
Date: Wed May 04 09:51:42 2016

Track NTP snippets data usage.

Adds new dependency edge components/{ntp_snippets => data_use_measurement/core}.

BUG= 601380 

Review-Url: https://codereview.chromium.org/1937003002
Cr-Commit-Position: refs/heads/master@{#391468}

[modify] https://crrev.com/4bbaba9313c70ca1b5f332ce4458192335d2f14d/components/ntp_snippets.gypi
[modify] https://crrev.com/4bbaba9313c70ca1b5f332ce4458192335d2f14d/components/ntp_snippets/BUILD.gn
[modify] https://crrev.com/4bbaba9313c70ca1b5f332ce4458192335d2f14d/components/ntp_snippets/DEPS
[modify] https://crrev.com/4bbaba9313c70ca1b5f332ce4458192335d2f14d/components/ntp_snippets/ntp_snippets_fetcher.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/353317e96cf335ebc2b4fc93cae387fec0d0ab58

commit 353317e96cf335ebc2b4fc93cae387fec0d0ab58
Author: treib <treib@chromium.org>
Date: Thu Jul 14 09:21:40 2016

Add NTPSnippets to DataUse.Service.Types histogram suffix

The NTPSnippets entry was originally added in https://codereview.chromium.org/1875073002, which added an enum entry in histograms.xml. Turns out there's also a suffix that needs to be updated.

BUG= 601380 

Review-Url: https://codereview.chromium.org/2138793002
Cr-Commit-Position: refs/heads/master@{#405455}

[modify] https://crrev.com/353317e96cf335ebc2b4fc93cae387fec0d0ab58/tools/metrics/histograms/histograms.xml